1. Field of the Invention
The present invention relates to a recording-medium storage device and an image forming apparatus.
2. Description of the Related Art
A recording-medium storage device (e.g., a paper feed tray) installed in an image forming apparatus is used to stack a recording medium (hereinafter, “paper”) and feed the paper to the image forming apparatus such that an image is formed thereon. The recording-medium storage device implements a stacking position determining mechanism for a paper stack. The stacking position determining mechanism includes edge guiding units, viz., an end fence and a plurality of side fences. The side fences guide the lateral edges of the paper stack with respect to a feeding direction, while the end fence guides the rear edge of the paper stack with respect to the feeding direction. The stacking position determining mechanism enables a user to precisely determine the position of the paper stack thereby preventing image misalignment on the paper or incorrect feed timing of the paper.
Recently, a universal paper feed tray compatible to various paper sizes has become mainstream. Such a universal paper feed tray enables the user to stack paper of different paper sizes for image formation. Consequently, user-friendliness is a critical issue while using a universal paper feed tray.
Conventionally, there are two position determining mechanisms corresponding to standard paper sizes. One mechanism is a notching mechanism in which a notch engagement is provided at a position corresponding to each standard paper size. The other mechanism is a latching mechanism (free stop mechanism), as disclosed in Japanese Patent Application Laid-open No. 2001-310824, in which a multiple latch engagement is provided for arbitrarily determining a position corresponding to the paper size. Generally, a conventional recording-medium storage device implements either one of the notching mechanism and the latching mechanism.
The notching mechanism suffices the needs of a user who mainly uses paper of standard paper sizes for image formation. However, the notching mechanism is not suitable for a professional user who uses paper of a free paper size. On the other hand, the latching mechanism is suitable for paper of standard paper sizes as well as a free paper size. Moreover, by using the latching mechanism, the user can reliably guide the edges of the paper stack. However, in that case, it is a requisite that the paper stack is neatly aligned to prevent problems such as image misalignment on the paper or incorrect feed timing of the paper.
Recently, a paper feed tray as disclosed in Japanese Patent Application Laid-open No. 2006-188357, which automatically recognizes the paper size of the paper stack by detecting the position of each edge guiding unit, is being increasingly used. As the paper sizes recognizable by the paper feed tray increase, it becomes more necessary to precisely lock the edge guiding units at desired positions corresponding to the standard paper sizes. Thus, the notching mechanism is more effective in such a case. However, as described above, the notching mechanism is not suitable for determining the positions of the edge guiding units corresponding to a free paper size. That is, it is difficult to determine positions of the edge guiding units corresponding to the standard paper sizes as well as a free paper size. Moreover, even if the edge guiding units are locked at a position corresponding to any paper size, it is necessary to maintain high operability while locking the edge guiding units at a particular position or moving them to another position.